Welding Filler Metal

A filler metal is a metal added in the making of a joint through welding, brazing, or soldering. Four types of filler metals exist—covered electrodes, bare electrode wire or rod, tubular electrode wire and welding fluxes. Sometimes nonconsumable electrodes are included as well, but since these metals are not consumed by the welding process, they are normally excluded.

Filler metals are an alloy or pure metal which, when heated, liquefies and melts to flow onto the space between two close fitting parts, creating a brazed or soldered joint. A filler metal has suitable melting and flow properties to permit distribution by capillary attraction in properly prepared joints. Filler metals produce joints that meet service requirements, such as strength and corrosion resistance.

In tig welding, the filler rod is fed into the molten puddle by hand. The choice of filler rod is extremely important as the rod must correctly match the material and alloy you will be welding. The thickness of the material to be welded determines the diameter of the filler rod.

Standard filler metals include tin, lead, silver, lead-free, cadmium-free, sil- phos, copper, aluminum, nickel, and jewelers gold. Filler metals are found in solid form like rings and wire, slugs, washers, powder, and paste. Fusion filler metals are atomized into powder form and include with flux in a paste composition.

Here are some good rules of thumb to help you select the correct filler metal:

1. 4043 is a good general filler metal for most aluminum applications. Remember 2xxx and 7xxx series aluminum is generally not recommended if the application requires welding.
2. 5356 is used for 5xxx series aluminum and is generally preferred if the finished piece will be anodized.
3. ER70S-6 is generally used for mild steel welding.
4. ER70S-2 is highly recommended for welding 4130 chrome-moly tubing in many applications.
5. ER80S-D2 is recommended for welding 4130 chrome-moly tubing if a higher strength, less ductile weld is required. If your weld will be heat treated to obtain optimum strength, then use a filler metal which matches the chemistry of your tubing, which neither 70S-2 nor 80S-D2 wires do.
6. Generally speaking, use a 1/16” diameter filler rod for applications where the material is 1/8” and less. Use a 3/32” diameter rod for 1/8” and thicker.